The present invention relates to a cylinder lock. More particularly this invention concerns such a lock having tumbler plates and a mechanical key.
A standard cylinder lock has a stationary cylinder housing and a core rotatable about an axis in the housing and formed with an axially extending key passage and a plurality of transverse guide slots. Respective tumbler plates transversely displaceable in the slots are each formed with a control edge exposed in the passage. Each plate is displaceable by a key from a freeing position to a blocking position that prevents rotation of the core in the housing. The key has a plurality of respective bits engageable with the control edges on axial engagement of the key in the passage. When the key is fully inserted in the passage all the plates are in the freeing position and the core can rotate in the housing.
Since much of the mechanism is actually held in the core, such a lock can be made very compact. Still the security offered is modest, particularly against picking.
It is therefore an object of the present invention to provide an improved cylinder lock.
Another object is the provision of such an improved cylinder lock which overcomes the above-given disadvantages, that is which is very secure and hard to pick.
A lock has according to the invention a stationary cylinder housing and a core rotatable about an axis in the housing and formed with an axially extending key passage, a plurality of transverse guide slots, and an axially inwardly open bore. A bolt is axially displaceable in the bore between a locked position and a retracted unlocked position and has a plurality of radially open grooves aligned transversely with the slots in the locked position of the bolt. The end of the bolt or a latch member, e.g. a ball, actuated by the bolt end can be pushed out in the locked position into a seat in the housing to rotationally fix the core in the housing. Respective tumbler plates transversely displaceable in the slots are each formed with a control edge exposed in the passage and a hole alignable with the bore in a freeing position of the respective plate. Each plate is displaceable from the freeing position to a blocking position with its hole offset at least partially from the bore and engaging in the respective groove to block axial movement of the bolt from the locked position. A key has a plurality of respective bit notches engageable with the control edges on axial engagement of the key in the passage. The control edges and the respective bit notches are positioned such that when the key is fully inserted in the passage all the plates are in the freeing position and the bolt can shift axially between its locked and unlocked positions.
Thus with this system the bolt can only retract and free the core to rotate when all of the tumbler plates are shifted into the freeing position. It is not possible to work the tumblers back one at a time with a flat pick as in the prior-art locks, and there is no way to get at the bolt from outside the lock.
According to the invention the bolt has an inner end that projects from the core housing in the locked position. The housing is formed with a seat complementarily engaging the inner end in the locked position.
The housing can be formed with one or more radially inwardly open seats and each plate is formed with a radially outwardly projecting tab engaged in the seat in the blocking position. Thus the plates help arrest the core in the housing.
Each plate is formed according to the invention with a guide formation engaging a complementary guide formation of the respective slot for transverse sliding of the tabs between the freeing and blocking positions. Alternately, a pivot is provided for rocking of the tabs between the freeing and blocking positions. In either case, respective springs urge the control edges toward the passage and, when a key is therein, into engagement with the key.
The bit notches in accordance with the invention end generally at a symmetry plane of the key. Furthermore they have flanks forming acute angles with the respective faces of the key so that, as the key is inserted in the passage, the control edges slide down into and then up out of the bit notches. In addition the key has a pointed front end cammingly engageable with the control edges on insertion of the key into the passage. The notches are provided in two sets staggered on opposite faces of the key. For ease of use the key is symmetrical to a plane and formed with two identical sets of notches for use of the key upside down.